Cardiogenic Shock

What is Cardiogenic Shock?

Cardiogenic shock occurs as a result of reduced pumping ability of the suddenly weakened heart due to various causes, such as damage to the muscles of heart from a severe heart attack; this results in insufficient blood being pumped out and not meeting the body’s requirements. Since the heart is not able to pump out all the venous return coming to it, it leads to the congestion of the lungs and viscera, and hence the condition is called congested shock.

The condition is a medical emergency and is fatal if not treated right away. It is a stage of end organ hypoperfusion which sets in due to the cardiac failure. It occurs in five to eight percent of the people admitted due to ST-elevation myocardial infarction. It is the most common cause of death in hospitalization due to heart attack.

What is the Pathophysiology of Cardiogenic Shock?

Most of the patients have multiple vessel coronary artery disease with decreased blood supply (ischemia) to the heart muscle (myocardium) resulting in its death (necrosis).

The impaired left ventricular filling causes back flow of blood into the lungs resulting in pulmonary edema and impaired gas exchange leading to low oxygen levels in the blood (hypoxemia).

The loss of viable heart muscle further causes heart muscle dysfunction aggravating the ischemia of the myocardium.

The resulting decreased cardiac output and blood flow to various vital organs leads to multiple organ dysfunction which may result in death.

Three organs of vital importance are the brain, heart, and kidneys. Reduced blood flow to the brain can result in altered sensorium and coma. Heart dysfunction and reduced cardiac output further aggravates the hypoperfusion state. Reduced blood flow to the kidneys reduces urinary output and ultimately kidney failure.

Additionally, ischemia of heart muscle followed by restoration of blood flow can cause systemic inflammation and sepsis due to relocation of intestinal bacteria and bacterial toxins contributing to increased mortality.

What are the Causes of Cardiogenic Shock?

Myocardial infarction or heart attack with left ventricular failure involving more than forty percent of the left ventricular myocardium forms the commonest cause of cardiogenic shock.

Factors which complicate myocardial infarction and precipitates cardiogenic shock include rupture of papillary muscle and the inter ventricular septum.

Mitral and aortic stenosis: again, the stenosed valve causes reduced blood flow to the body and the hypoperfusion leads to shock

Congestive heart failure: is in itself a state of hypoperfusion where enough blood is not pumped to meet the body’s needs.

Severe valvular dysfunctions like acute aortic regurgitation, acute mitral regurgitation also have an adverse effect on the amount of blood pumped out by the left ventricle per minute.

Acute massive pulmonary embolism: causes a block in the blood vessels of the lungs, thereby decreasing the amount of blood entering the heart and eventually decreaseing the amount of blood that gets distributed in the body, and hence creates a state of hypoperfusion.

Pericardial tamponade: In a massive cardiac tamponade, fluid is filled in the membranes covering the heart, and in turn compressing it; the heart is thus unable to pump out adequate blood to the body, and hence creating hypoperfusion.

Cardiac arrhythmias.

Toxic states of heart.

Dilated cardiomyopathy.

Cardiac tumours.

What are the Signs and Symptoms of Cardiogenic Shock?Decrease in the tissue and organ blood flow leads to multiple organ system failure and the signs and symptoms are categorized organ wise as follows:

GIT: Hemorrhage is seen

Skeletal muscles:

Lactic acidosis: Decreased tissue perfusion leads to reduced oxygenation and anaerobic cycle of energy production sets in the body, where lactic acid is the end product of glucose, which is used to break down to release energy for bodily needs. Accumulation of lactic acid leads to lactic acidosis and is harmful for the body

Liver and kidney functions are assessed to determine the functional status of these organs

3. The diagnosis is confirmed by the following:

Electrocardiography (ECG): An ECG may show evidence of myocardial ischemia such as ST-segment elevation, ST-segment depression, or Q waves. A normal ECG however does not rule out presence of ischemia.

Echocardiography: It is necessary to perform an echocardiogram to find out the cause of the cardiogenic shock. It may reveal akinetic or dyskinetic areas of heart muscle and valvular pathology. Left ventricular ejection fraction (LVEF) can also be measured.

Pulmonary artery (PA) catheterization: Pulmonary artery catheter is a balloon tipped catheter that is inserted in the artery carrying away the blood from the heart to the lungs. It was initially used in the management of myocardial infarction. It measures the pressure in the artery going into lungs from the heart, oxygen saturation in the blood, blood pumped out by the left ventricle per minute, blood pumped out by the left ventricle per heartbeat, and the pressure in the capillary network of lungs.

How do you Treat Cardiogenic Shock?The medical treatment of cardiogenic shock can be monitored for its efficacy by measuring the changes in cardiac output and left ventricular filling pressure, both before and after the administration of various vasopressor, inotropic, and volume expansion drugs and altering the dosage and frequency accordingly.

General measures

Drug therapy

Reperfusion therapy

Surgical therapy

1. Patient monitoring

Clinical monitoring of pulse, blood pressure and respiration

Measure arterial blood gases and pH for correction of acidosis and hypoxia

Pulmonary capillary wedge pressure monitoring

Monitoring hourly urinary output

2. General measures

Care of the skin, airway, bowel and bladder, and nutrition as the patient requires prolonged hospitalization

Relieve pain by intravenous morphine sulfate

Put the patient in a propped up position, which is the most comfortable position to relieve shortness of breath

Correction of hypoxia is done by oxygen face masks or nasal prongs, and if necessary, by intubation and mechanical ventilation devices

Acidosis is treated with intravenous sodium bicarbonate infusion

3. Drug Therapy

Drugs must be used only after correcting the volume deficit and heart rate. They act by increasing the cardiac output and allow better perfusion and redistribution of blood flow to vital organs like kidneys, heart and brain. The drugs used are:

Cardiogenic shock can be both treated and prevented by very early re-perfusion therapy for myocardial infarction. Early revascularization for cardiogenic shock improves survival drastically.

Drugs used are:

Clopidogrel may also be used

Thrombolytics are agents that dissolve clots and restore blood flow to the heart. These are generally given when emergency heart catheterization facilities are not available

Medical Procedures - these aim to restore blood flow to the heart and include

Angioplasty and stenting - If a block in the coronary vessel is found, a long thin tube (catheter) with a special balloon is inserted via the artery in the thigh and once in position, the balloon is inflated to open up the blockage. A metal stent may be placed in the artery to maintain its patency. In many cases the stent is coated with medication that releases slowly and helps to keep the vessel open.

Intra-aortic balloon counterpulsation (IABP) - A balloon is placed in the major vessel, the aorta. It inflates when the heart relaxes and deflates when the heart contracts. It improves the perfusion to both the heart muscles as well as to the entire body. It increases the left ventricle performance by alternating inflation and deflation.

5. Surgical therapy

Circulatory assist devices: these may be beneficial in selected cases of cardiogenic shock. The various modalities included are:

Partial cardiac bypass (left ventricle assist devices)

Coronary artery Bypass surgery – The surgery is done to restore blood flow in a blocked coronary vessel. Grafts from saphenous vein in the leg or the artery on the chest wall are taken and attached to the coronary vessel beyond the block. The distal end of the graft is attached to the aorta.

Other conditions requiring surgery

It aims to correct the underlying cause. It is indicated in following cases

Ruptured papillary muscle

Acute mitral regurgitation

Rupture of the interventricular septum

Acute aortic regurgitation

Aortic dissection

Acute massive pulmonary embolism

How do you Prevent Cardiogenic Shock?The ideal way to prevent cardiogenic shock is to prevent a heart attack, which could be achieved by the following measures:

Eat a healthy and a balanced diet. Eat a diet low in cholesterol and fats

Diabetic patients must maintain their sugar levels in the normal range and take the medicines regularly

Avoid stress and hectic schedules

Maintain a healthy sleep pattern

Inspite of these preventive measures, if an acute myocardial infarction occurs, immediate hospitalization and administration of early revascularization and reperfusion therapies might prevent the advent of cardiogenic shock

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